The present application generally relates to the field of grinding workpieces. More specifically, the invention is related to the field of centerless grinding. Still more specifically, the invention is related to a grinding machine for centerless grinding of workpieces disposed on a support in the area of a longitudinal plane of the grinding machine, comprising a first slide for a grinding wheel positioned laterally relative to the longitudinal plane, a second slide for a regulating wheel being likewise positioned laterally with respect to the longitudinal plane, a first dressing tool for dressing the grinding wheel at a first predetermined position and a second dressing tool for dressing the regulating wheel at a second predetermined position.
A grinding machine of the type specified before is disclosed in EP 0 448 509 B1.
In this prior art grinding machine the grinding wheel and the regulating wheel are disposed on opposite sides of a longitudinal median plane of the grinding machine, as is conventionally known. In the area of the longitudinal median plane, i.e. between the grinding wheel and the regulating wheel, a support rail is disposed in an axial extension along the longitudinal median plane for supporting the workpieces to be ground. The support rail, as is also well-known per se, is configured sloped at its upper surface. It may be displaced vertically.
The grinding wheel and the regulating wheel together with their associated drives are each disposed on slides. These slides are configured to be displaced both parallel to the longitudinal median plane, along the so-called Z-axis as also along a direction extending under right angles thereto and conventionally designated as X-axis. Moreover, they may be pivoted about a vertical axis.
In this prior art grinding machine, one separate dressing tool each is provided for the grinding wheel on the one hand and for the regulating wheel on the other hand. The dressing tools are positioned on the respective associated slides and extend parallel to the X-axis. The dressing tools engage the grinding wheel and the regulating wheel, respectively, at their respective rear sides, i.e. at the side that is opposite to the longitudinal median plane and, hence, opposite to the workpiece.
The prior art machine has, therefore, the disadvantage that an additional space is necessary on the rear side of the grinding wheel and of the regulating wheel allowing to position the dressing tools in that area. Besides this disadvantage under design aspects, the prior art grinding machine has the essential functional disadvantage that due to the rearward position of the dressing tools precision problems may be generated. These problems are generated on the one hand due to temperature variations as a consequence of different expansions of machine sections, but in particular when the grinding wheel and/or the regulating wheel are pivoted about the vertical axis (so-called B-axis) and/or about an axis (so-called A-axis) extending parallel to the X-axis. These pivotal movements are necessary because the axial feed force is generated by pivoting the regulating wheel about the A-axis, whereas pivoting the regulating wheel about the B-axis the workpiece is directed radially relative to the grinding wheel so as to allow predetermining a desired cylindrical or conical shape.
If now the grinding wheel and the regulating wheel are dressed xe2x80x9cfrom behindxe2x80x9d, geometric errors are inevitably generated when errors occur during the pivotal movement about the A-axis and/or the B-axis. These dressing errors, in turn, result in contour errors on the worked workpieces which, again, can only be corrected by a complicated iterative readjustment of the A-axis and the B-axis.
WO 96/05940 discloses an external cylindrical surface grinding machine in which the workpieces are chucked between tips. In this prior machine tool, two grinding wheels are provided one besides of the other. The two grinding wheels together with their associated drives are each seated on a separate slide. The slides, in turn, may be displaced along the X- and the Z-direction.
Both slides of this prior art grinding machine are provided with dressing rollers. By appropriately advancing and retracting the dressing rollers and by approaching the two slides with respect to each other, the dressing roller on the one slide will dress the grinding wheel on the other slide and vice versa. However, also in this prior art grinding machine the dressing rollers are positioned on the rear side of the grinding wheels, i.e. on the side opposite the workpiece.
For that reason also this prior art grinding machine has the disadvantage mentioned above.
Another grinding machine for centerless grinding is disclosed in EP 0 616 870 A1. In this prior art grinding machine, dressing tools for the grinding wheel and the regulating wheel, respectively, are positioned in front of the slide carrying the grinding wheel and its associated drive. One of the dressing tools is stationary and the other dressing tool may be transported on the respective other slide.
Further, EP 0 449 767 A1 discloses a grinding machine for centerless grinding of still more conventional design having dressing tools on the side of the grinding wheel and the regulating wheel, respectively, opposite the center median plane.
It is, therefore, an object underlying the invention to improve a grinding machine of the type specified at the outset and being intended to be used for centerless grinding of workpieces, such that the disadvantages mentioned above are avoided. In particular, the dressing of the grinding wheel and/or of the regulating wheel shall become possible without sacrificing further space on the machine. In particular, the invention shall make it possible to perform dressing on the wheels without any contour errors on the workpiece at all or with only negligible such contour errors, even if the machine is subjected to varying temperatures and/or positioning errors should occur during the pivotal movement about the A- and/or B-axis.
According to the grinding machine specified at the outset, this object is achieved in that the positions are located in the area of the longitudinal plane.
The object underlying the invention is thus entirely solved. If, namely, the positions are in the area of the longitudinal plane, this means that the dressing process occurs in the area of engagement of the wheels (grinding wheel and regulating wheel), i.e. essentially at the point where the two wheels are in contact with the workpiece during a machining operation.
This has the essential advantage that the entire assembly is concentrated in the area of the longitudinal median plane, in particular in front of the wheels, so that no additional space is required behind the grinding wheels and their associated drives, respectively. Above all, the invention has the advantage that the contour errors explained above are minimized and, mostly, entirely eliminated because the dressing operation is effected at a position where the later engagement of the workpiece takes place. Therefore, for simply geometric reasons no errors of the type discussed above may occur.
The precision of the grinding machine may, hence, be substantially improved with relatively simple design measures.
In preferred embodiments of the invention, the longitudinal plane is the longitudinal median plane of the grinding machine, wherein, as known per se, the slides may be disposed on opposite sides of the longitudinal median plane.
This measure has the advantage that the dressing tools are disposed between opposite wheels so that no further space is required.
In further embodiments of the invention, kinematic variations and inversions of the sequence of motion of the various elements involved are possible.
For example, according to an embodiment of the invention, it is possible to make the first and/or the second dressing tool displaceable.
According to a first variation of this embodiment, this is made by disposing the first and/or the second dressing tool on a third slide which, preferably, is adapted to be displaced along an axis extending parallel to the longitudinal plane.
This measure has the advantage that the dressing movement is effected along the Z-axis by displacing the third slide, so that the first and the second slide for the grinding wheel and for the regulating wheel must not be displaced during the dressing operation. It is particularly preferred in this context when the two slides are not adapted to be displaced at all along the Z-axis which is sufficient for many applications with respect to the processing of the workpieces so that a substantial simplification of the machine is obtained which, in turn, results in lower manufacturing costs.
According to another variant of this embodiment, the first and/or the second dressing tool may, however, also be disposed on the respective other slide, i.e. the first dressing tool may be disposed on the second slide and/or the second dressing tool may be disposed on the first slide.
This measure has the advantage that the dressing process is effected by simply utilizing machine axes so that no separate drives are necessary for the dressing assembly (separate dressing axis or axes, respectively).
According to another modification of this variant, the respective dressing tool is disposed on a movable arm such that the dressing tool preferably is positioned within the peripheral contour of the regulating wheel or the grinding wheel, respectively, and outside that peripheral contour when in a dressing position.
This measure has the advantage that the sequence of motion may be simplified and that collisions between the dressing tool and the respective other slide or the respective other dressing tool or the workpiece may be avoided because when the dressing tool is not needed, it will be displaced into its retracted position.
In this embodiment it is further preferred when the arm is adapted to be pivoted about an axis or is adapted to be shifted along an axis.
It had already been mentioned that the displaceability of the dressing tools on the one hand and of the slides on the other hand depend on each other. In any case it is necessary to ensure a relative displaceability with respect to the X-axis and the Y-axis.
If, according to the above-discussed embodiments of the invention, the dressing tools are disposed on the slide and the dressing operation is executed by reciprocally approaching the slides relative to one another, similarly as discussed in WO 96/05940 discussed at the outset, it is necessary that the slides are adapted to be displaced not only along the Z-axis but also along the X-axis.
According to further embodiments of the invention, the first dressing tool is disposed stationarily and the first slide is adapted to be displaced along a first axis extending parallel to the longitudinal plane as well as along a second axis extending under right angles relative to the longitudinal plane.
This measure, too, has the advantage that the dressing operation may be executed solely by making displacements along the machine axes without the necessity of separate dressing axes.
According to this embodiment of the invention it is further preferred when the first and/or the second dressing tool and the support are structurally integrated on a common console.
This measure has the advantage that the components that are provided in the area of the longitudinal median plane anyway, are utilized for several purposes, namely when the console is utilized for supporting the support on the one hand and, on the other hand, serves as a basis for one or two dressing tools.
Correspondingly or alternatively or in addition, the machine may be configured such that the first and/or the second dressing tool together with a feeding assembly for the workpieces are structurally integrated on a common console.
According to further embodiments of the invention, it is preferred when the axes of the grinding wheel and of the regulating wheel lie in the same plane as the points of engagement of the dressing tools on the grinding wheel and on the regulating wheel.
This measure has the advantage already mentioned at the outset that a very high precision may be obtained when the grinding wheel and the regulating wheel are dressed exactly at the same position where they come into engagement with the workpiece at a later moment in time.
The same holds true if according to a preferred variation of this embodiment, as known per se, the plane is disposed below the points of engagement of the grinding wheel and the regulating wheel on the workpiece by a predetermined amount. In exceptional cases, however, it may also be disposed above these points of engagement.
Moreover, embodiments of the invention are preferred in which not two separate dressing tools are utilized but, instead, the first and the second dressing tool are structurally integrated into a common dressing tool.
This method has the advantage that the machine is less complicated and the dimensions of the grinding machine may be reduced.
The grinding machine according to the present invention may be used for various centerless grinding processes, namely for external cylindrical surface grinding, internal cylindrical surface grinding, plunge grinding or angular plunge grinding.
It goes without saying that the features mentioned before and those that will be explained hereinafter, may not only be used in the particularly given combination, but also in other combinations or alone, without leaving the scope of the present invention.